1. Field of the Invention
This invention relates to a binarization method of binarizing an image by extracting lightness (brightness, density) as a feature amount from the image, and an image processing system using the method.
2. Description of the Related Art
In extraction processing intended for extracting an object from an image, it is important to discriminate areas contained in the image from each other. In a method of discriminating the areas, it is common practice to discriminate the image as a partial image having uniform feature amounts of lightness, color, texture, and the like.
The method of recognizing the areas with the lightness as the feature amount is already used in various industrial fields; for example, it is applied to determination as to whether or not the title lettering of a product exists, determination of the front or back of a part, inspection on parts for loss, inspection for dirt and flaw, and the like.
In a system for such purposes, an image of the object such as a product is picked up using an image pickup machine such as a camera and the picked-up image is input to an image processing system as an analog signal comprising Y values representing the lightness for each pixel, then the analog Y values input are converted into digital Y values, which then are stored in a storage unit. The image processing system displays the original image on a display unit such as a CRT based on the stored information.
By the way, to execute the determination and inspection as described above, normally a binary image is used, thus hitherto it has been common practice to directly enter a numeric value for the displayed image through an input unit from the outside, thereby binarizing the displayed image with the entered numeric value as a threshold value.
However, in the method as described above, the lightness (brightness) to be extracted is entered in a numeric value, thus it is sensuously difficult to associate the entered numeric value with the lightness corresponding thereto. This results in extreme difficulty particularly if the lightness difference in the original image is small.
It is therefore an object of the invention to provide an image binarization method wherein a pixel to be extracted on a screen can be directly selected sensuously easily without the need for setting a threshold value in a numeric value, and to provide an image processing system using the method.
According to a first aspect of the invention, there is provided an image binarization method comprising the steps of setting a threshold value range for a value concerning a Y value representing brightness of a pixel selected from an image and extracting a pixel with the value concerning the Y value in the image within the threshold value range, wherein when a pixel is selected in the image, the threshold value range is set in a range of adding a predetermined value to the value concerning the Y value of the selected pixel and/or subtracting the predetermined value therefrom, and wherein when after the pixel is selected, a pixel different from that pixel is selected, if the value concerning the Y value of the selected pixel is greater than the value concerning the Y value of the pixel for which the threshold value range is set, between the predetermined value added to the value concerning the Y value of the selected pixel and a lower limit value in the threshold value range, a new threshold value range is set, or if the value concerning the Y value of the selected pixel is smaller than the value concerning the Y value of the pixel for which the threshold value range is set, between the predetermined value subtracted from the value concerning the Y value of the selected pixel and an upper limit value in the threshold value range, a new threshold value range is set.
According to a second aspect of the invention, there is provided an image binarization method comprising the steps of setting a threshold value range for a value concerning a Y value representing brightness of a pixel selected from an image and extracting a pixel with the value concerning the Y value in the image within the threshold value range, wherein when an unextracted pixel is selected, the threshold value range is set in a range of adding a predetermined value to the value concerning the Y value of the selected unextracted pixel and/or subtracting the predetermined value therefrom, and wherein when an already extracted pixel is selected, if the value concerning the Y value of each of one or more unextracted pixels of pixels in a predetermined range containing the already extracted pixel selected is greater than an upper limit value in the threshold value range, using the value concerning the Y value of the unextracted pixel with the minimum difference between the value concerning the Y value of each of one or more unextracted pixels and the upper limit value in the threshold value range as an upper limit value, a new threshold value range is set, or if the value concerning the Y value of each of one or more unextracted pixels of pixels in a predetermined range containing the already extracted pixel selected is smaller than a lower limit value in the threshold value range, using the value concerning the Y value of the unextracted pixel with the minimum difference between the value concerning the Y value of each of one or more unextracted pixels and the lower limit value in the threshold value range as a lower limit value, a new threshold value range is set.
According to a third aspect of the invention, there is provided an image processing system for setting a threshold value range for a value concerning a Y value representing brightness of a pixel selected from an image and extracting and displaying a pixel with the value concerning the Y value in the image within the threshold value range, the image processing system comprising: first threshold value setting means, when a pixel is selected in the image, for setting the threshold value range in a range of adding a predetermined value to the value concerning the Y value of the selected pixel and/or subtracting the predetermined value therefrom; and second threshold value setting means, when after the pixel is selected, a pixel different from that pixel is selected, if the value concerning the Y value of the selected pixel is greater than the value concerning the Y value of the pixel for which the threshold value range is set, between the predetermined value added to the value concerning the Y value of the selected pixel and a lower limit value in the threshold value range, the second threshold value setting means for setting a new threshold value range, or if the value concerning the Y value of the selected pixel is smaller than the value concerning the Y value of the pixel for which the threshold value range is set, between the predetermined value subtracted from the value concerning the Y value of the selected pixel and an upper limit value in the threshold value range, second threshold value setting means for setting a new threshold value range.
According to a fourth aspect of the invention, there is provided an image processing system for setting a threshold value range for a value concerning a Y value representing brightness of a pixel selected from an image and extracting and displaying a pixel with the value concerning the Y value in the image within the threshold value range, the image processing system comprising: first threshold value setting means, when an unextracted pixel is selected, for setting the threshold value range in a range of adding a predetermined value to the value concerning the Y value of the selected unextracted pixel and/or subtracting the predetermined value therefrom; and second threshold value setting means, when an already extracted pixel is selected, if the value concerning the Y value of each of one or more unextracted pixels of pixels in a predetermined range containing the already extracted pixel selected is greater than an upper limit value in the threshold value range, the second threshold value setting means using the value concerning the Y value of the unextracted pixel with the minimum difference between the value concerning the Y value of each of one or more unextracted pixels and the upper limit value in the threshold value range as an upper limit value for setting a new threshold value range, or if the value concerning the Y value of each of one or more unextracted pixels of pixels in a predetermined range containing the already extracted pixel selected is smaller than a lower limit value in the threshold value range, the second threshold value setting means using the value concerning the Y value of the unextracted pixel with the minimum difference between the value concerning the Y value of each of one or more unextracted pixels and the lower limit value in the threshold value range as a lower limit value for setting a new threshold value range.
According to a fifth aspect of the invention, there is provided an image processing system for setting a threshold value range for a value concerning a Y value representing brightness of a pixel selected from an image and extracting and displaying a pixel with the value concerning the Y value in the image within the threshold value range, the image processing system comprising: storage means for storing a history of a selected pixel; first threshold value setting means, when a pixel is selected in the image based on the storage result of the storage means, for setting the threshold value range in a range of adding a predetermined value to the value concerning the Y value of the selected pixel and/or subtracting the predetermined value therefrom; and second threshold value setting means, when after the pixel is selected, a pixel different from that pixel is selected, if the value concerning the Y value of the selected pixel is greater than the value concerning the Y value of the pixel for which the threshold value range is set, between the predetermined value added to the value concerning the Y value of the selected pixel and a lower limit value in the threshold value range, the second threshold value setting means for setting a new threshold value range, or if the value concerning the Y value of the selected pixel is smaller than the value concerning the Y value of the pixel for which the threshold value range is set, between the predetermined value subtracted from the value concerning the Y value of the selected pixel and an upper limit value in the threshold value range, second threshold value setting means for setting a new threshold value range.
According to a sixth aspect of the invention, there is provided an image processing system comprising: selection means for operating a displayed pointer superimposed on an image and selecting a target pixel from the image; threshold value setting means for setting a threshold value range for a value concerning a Y value representing brightness of the pixel; extraction means for extracting a pixel with the value concerning the Y value in the image within the threshold value range; display means for displaying the extraction result; storage means for storing a history of a selected pixel; first threshold value setting means, when a pixel is selected in the image based on the storage result of the storage means, for setting the threshold value range in a range of adding a predetermined value to the value concerning the Y value of the selected pixel and/or subtracting the predetermined value therefrom; and second threshold value setting means, when after the pixel is selected, a pixel different from that pixel is selected, if the value concerning the Y value of the selected pixel is greater than the value concerning the Y value of the pixel for which the threshold value range is set, between the predetermined value added to the value concerning the Y value of the selected pixel and a lower limit value in the threshold value range, the second threshold value setting means for setting a new threshold value range, or if the value concerning the Y value of the selected pixel is smaller than the value concerning the Y value of the pixel for which the threshold value range is set, between the predetermined value subtracted from the value concerning the Y value of the selected pixel and an upper limit value in the threshold value range, second threshold value setting means for setting a new threshold value range.
According to a seventh aspect of the invention, there is provided an image processing system for setting a threshold value range for a value concerning a Y value representing brightness of a pixel selected from an image and extracting and displaying a pixel with the value concerning the Y value in the image within the threshold value range, the image processing system comprising: storage means for storing a history of an extracted pixel; first threshold value setting means, when an unextracted pixel is selected based on the storage result of the storage means, for setting the threshold value range in a range of adding a predetermined value to the value concerning the Y value of the selected pixel and/or subtracting the predetermined value therefrom; and second threshold value setting means, when an already extracted pixel is selected, if the value concerning the Y value of each of one or more unextracted pixels of pixels in a predetermined range containing the already extracted pixel selected is greater than an upper limit value in the threshold value range, the second threshold value setting means using the value concerning the Y value of the unextracted pixel with the minimum difference between the value concerning the Y value of each of one or more unextracted pixels and the upper limit value in the threshold value range as an upper limit value for setting a new threshold value range, or if the value concerning the Y value of each of one or more unextracted pixels of pixels in a predetermined range containing the already extracted pixel selected is smaller than a lower limit value in the threshold value range, the second threshold value setting means using the value concerning the Y value of the unextracted pixel with the minimum difference between the value concerning the Y value of each of one or more unextracted pixels and the lower limit value in the threshold value range as a lower limit value for setting a new threshold value range.
According to an eighth aspect of the invention, there is provided an image processing system comprising: selection means for operating a displayed pointer superimposed on an image and selecting a target pixel from the image; threshold value setting means for setting a threshold value range for a value concerning a Y value representing brightness of the pixel; extraction means for extracting a pixel with the value concerning the Y value in the image within the threshold value range; display means for displaying the extraction result; storage means for storing a history of an extracted pixel; first threshold value setting means, when an unextracted pixel is selected based on the storage result of the storage means, for setting the threshold value range in a range of adding a predetermined value to the value concerning the Y value of the selected pixel and/or subtracting the predetermined value therefrom; and second threshold value setting means, when an already extracted pixel is selected, if the value concerning the Y value of each of one or more unextracted pixels of pixels in a predetermined range containing the already extracted pixel selected is greater than an upper limit value in the threshold value range, the second threshold value setting means using the value concerning the Y value of the unextracted pixel with the minimum difference between the value concerning the Y value of each of one or more unextracted pixels and the upper limit value in the threshold value range as an upper limit value for setting a new threshold value range, or if the value concerning the Y value of each of one or more unextracted pixels of pixels in a predetermined range containing the already extracted pixel selected is smaller than a lower limit value in the threshold value range, the second threshold value setting means using the value concerning the Y value of the unextracted pixel with the minimum difference between the value concerning the Y value of each of one or more unextracted pixels and the lower limit value in the threshold value range as a lower limit value for setting a new threshold value range.
According to the image binarization method and the image processing systems using the method according to the first, third, fifth, and sixth aspects of the invention, when a pixel to be extracted is selected in an image, with a predetermined value added to the value concerning the Y value of the pixel and/or subtracted therefrom as a threshold value range, a pixel is extracted and after this, when a pixel different from that pixel is selected, the predetermined value is added to the value concerning the Y value of the pixel or is subtracted therefrom and a new threshold value range is set in the consecutive range between the calculation result and the already setup threshold value range, and a pixel is extracted based on the new setup threshold value range. Thus, different pixels can be selected one after another for widening the brightness extraction range stepwise, and the pixel to be extracted on the screen can be directly selected sensuously easily without the need for entering a numeric value for setting the threshold value range.
A specific description will be given with reference to schematic diagrams of FIGS. 11(a) to 11(e). For example, binarization sensitivity k is adopted as the predetermined value and a single value for the Y values is preset. When a pixel is selected in an image, the Y value of the pixel is set to Y1 and the sensitivity k is added to and subtracted from the value, thereby setting the xe2x80x9cthreshold value range of Y, Y1xe2x88x92k to Y1+kxe2x80x9d as indicated by the arrow in FIG. 11(a). The setting of the threshold value range according to the first, third, fifth, and sixth aspects of the invention is not limited to adding and subtracting the sensitivity k to and from Y1 as the center value; the sensitivity k can be only added to or subtracted from the value or one sensitivity can be added to the value and another sensitivity can be subtracted therefrom. However, not only a single value for the Y values as described above, but also an appropriate value based on the value concerning the Y value may be used as the sensitivity k in response to the situation, needless to say.
Next, brightness is extracted based on the setup threshold value range, whereby threshold value range of the Y value of the selected pixel minus the sensitivity k to the Y value of the selected pixel plus the sensitivity k can be set. Next, when a different pixel is selected in the image, the Y value of the pixel is set to Y2 and xe2x80x9cif Y1xe2x89xa6Y2, the threshold value range of Y is Y1xe2x88x92k to Y2+kxe2x80x9d as indicated by the arrows in FIGS. 11(b) and 11(d); xe2x80x9cif Y1 greater than Y2, the threshold value range of Y is Y2xe2x88x92k to Y1+kxe2x80x9d as indicated by the arrows in FIGS. 11(c) and 11(e). Further, when a different pixel is selected in the image, Y2 is assigned to Y1 and Y3, the Y value of the new selected pixel, is assigned to Y2, whereby setting of the threshold value range is repeated.
According to the image binarization method and the image processing systems using the method according to the second, fourth, seventh, and eighth aspects of the invention, when a pixel having the brightness to be extracted is selected, an unextracted pixel is selected from among the pixels in a predetermined range containing the selected pixel, a pixel most similar to the value concerning the Y value of the first selected pixel to be extracted is selected from among the selected extracted pixels, and the threshold value range is set based on the value concerning the Y value of the pixel for extracting a pixel. Thus, a similar brightness area can be stepwise extracted without changing the selected pixel.
If an unextracted pixel is selected as the pixel to be extracted, a threshold value range is set as in the image binarization method and the image processing systems using the method according to the first, third, fifth, and sixth aspects of the invention. If an already extracted pixel is selected, first an unextracted pixel is selected from among the pixels in a predetermined range containing the selected pixel and for the Y values of the selected unextracted pixels, offset amount Dy indicating the distance from the threshold value range Ty of the Y values, set for the selected pixels is calculated.
For example, if xe2x80x9cYxe2x89xa6lower limit value in Tyxe2x80x9d, xe2x80x9cDy=lower limit vale in Tyxe2x88x92Yxe2x80x9d; if xe2x80x9cY greater than upper limit value in Tyxe2x80x9d, xe2x80x9cDy=Yxe2x88x92upper limit vale in Tyxe2x80x9d. The operation is performed for all unextracted pixels and with the pixel corresponding to the minimum Dy as brightness most similar to the pixel to be extracted, the threshold value range is expanded so as to contain the Y value of the pixel, setting a new threshold value range.